Magic values, except for predefined, are forbidden in coding.
<p>Examples:</p>
<pre>
    Negative example:
    //Magic values, except for predefined, are forbidden in coding.
    if (key.equals("Id#taobao_1")) {
            //...
    }
    Positive example:
    String KEY_PRE = "Id#taobao_1";
    if (KEY_PRE.equals(key)) {
            //...
    }
</pre>